In light of the current state of heightened terrorism risk, an easily assessed, well-characterized and broadly applicable biodosimeter is urgently required in order to identify those personnel that may be susceptible to the morbidity and mortality associated with the pulmonary consequences of a mass radiological or nuclear event. Indeed, due to our increased ability to care for victims of acute accidental (or intentional) exposure, exposed persons are more likely to survive the immediate hematological crises which result from whole body exposure; however late morbidities then can occur as part of a multi-organ dysfunction syndrome. Therefore, the down- stream roles played by such organs as the lung in this syndrome's progression are of increasing concern and need to be identified in order to employ timely mitigation. We believe that we have identified a potential biomarker of radiation-induced lung late effect progression, Clara cell secretory protein (CCSP/CC16), which is expressed in an injury-specific pattern, identifiable in the plasma. In order to fully characterze this biomarker, we will make use of a pertinent 2-strain murine model, thereby covering the spectrum of lung endpoints seen in the human population. In addition, we will assess the differential expression pattern of the biomarker in two special populations, children and the elderly, through the use of neonate and aged mouse models. The three specific aims include: 1. To test the hypothesis that changes in the amount of Clara cell secretory protein (CCSP or CC16) versus surfactant protein-D (SP-D) expression in the plasma of irradiated animals will predict the incidence and progression of radiation fibrosis; 2. To test the specificity of the CCSP marker in other models of lung injury that result in an inflammatory and/or fibrotic response; 3. To determine the utility of CCSP as a marker of chronic lung injury in a special population. The value of such biomarkers exists both in their ability to predict the progression of disease following exposure and their usefulness in evaluating the efficacy of mitigation strategies that may be employed to prevent such injury. Importantly, the biomarkers being sought in this effort are markers of effect, and not markers of dose, thereby providing the additional information required before making critical decisions regarding potential interventions. We anticipate that by the end of the funding period, we will have identified the time- and dose-specific patterns of expression of CCSP, a biomarker that could potentially then be developed for use in both the immediate and delayed periods following a radiological event.